The present invention is directed to equipment used in metal forming operations, and specifically to equipment that automatically positions metal extrusions or shaped sheet in a modular die system for forming an offset pattern.
Sheet metal parts in the form of extrusions and shaped sheet are often used in aircraft structures for structural assemblies. These metal component parts are relatively thin, usually about {fraction (3/16)}xe2x80x3 maximum, and most typically between about xe2x85x9xe2x80x3 to about {fraction (1/16)}xe2x80x3 in thickness. The component parts may be thinner than {fraction (1/16)}xe2x80x3, the thickness being dictated by the application. These structural assemblies can be intricate internal assemblies or assemblies such as fuselage structures, wing structures, nacelles or thrust reversers. In order to properly assemble these structures, it is necessary to further form the extrusions and shaped sheet to have joints that permit proper fit-up as well as strength. These joints are formed by using a die assembly to form a joggle in the extrusion or shaped sheet.
A joggle is an offset in a flat plane consisting of at least two bends in opposite directions in which material is displaced into a new plane that is parallel to the original plane. The joggle forms a new plane from the original material that is substantially parallel to the plane of the original shaped sheet or extrusion. Joggles are formed by placing the shaped sheet metal or extrusions in a die to form the desired joint configuration. These joggles are then assembled to similar or identical joggles in mating parts that allow for proper fit-up and assembly of the mating parts. Typically, the dies are modular die systems. While the shaped sheet or extrusions may have joggles formed by cold working, that is, forming the joggle at ambient temperature, the joggles more frequently are formed by heating the workpiece to elevated temperatures by using heated dies.
Many of the sheet metal parts utilized in aircraft applications include titanium and titanium alloys as well as aluminum and aluminum based alloys such as aluminum alloy designated as 7075. Joggles are hot formed in extrusions and shaped sheet of this alloy by manually positioning the extrusion or shaped sheet in contact with a heated die in a forming press. The dies are modular and are interchangeable, the specific die system used depending upon the extrusion or shaped sheet that is supplied and the location and shape of the joggle required. The length of the extrusion or shaped sheet into which the joggle is to be formed is not restricted, although the joggle is typically formed near the end of the part. Typically, a joggle is formed within about two feet of one end of the extrusion or shaped sheet, as this is the location of fit-up with a mating part. However, the die system and forming press may be designed to form a joggle at greater distances from an end of the extrusion or shaped sheet.
The current practice for aligning an extrusion, shaped sheet or other workpiece in a forming press is for the operator to manually position the part inside of a preselected heated die. A combination square having a right angle and a scale along at least one edge is positioned against a die surface, and the workpiece is positioned adjacent to, or in contact with, the end of the scale on the combination square to allow the operator to properly align the workpiece in the forming press. This method is both inefficient and hazardous. It is hazardous as it requires the operator to perform hand alignment of the workpiece inside or adjacent to heating dies that have been heated to an elevated temperature, typically about 300xc2x0 F.-370xc2x0 F. for aluminum alloy 7075. The temperature will vary depending upon the alloy used, and may be higher or lower, but will always be sufficiently high for forming and capable of causing burns to a careless operator. In addition, proper alignment may entail the operator placing his/her hands within the die assemblies of the forming press, thereby exposing a careless operator to potential injury by placing hands within pinch points. In addition to the dangers with the present system, it is also inaccurate. The workpiece is aligned visually and by hand by an operator against a scale having linear gradations that are {fraction (1/32)}xe2x80x3 (0.031xe2x80x3) or {fraction (1/64)}xe2x80x3 (0.015xe2x80x3) apart, requiring the operator to estimate the correct location of the workpiece within the die. Furthermore, as the workpiece becomes longer and with a portion of the workpiece extending beyond the die, it becomes more difficult for the operator to correctly estimate the location of the portion of the workpiece into which the joggle is to be formed as the operator must attempt to align a location marker applied to the workpiece with a parting line in the die that is used to form the joggle. Not only is the system limited by the instrumentation, but also additional error easily can be introduced by failure of the operator to properly align the workpiece against the scale. Clearly, due to the inherent inaccuracies, the current system can reasonably be controlled from about {fraction (1/64)}xe2x80x3 to about {fraction (1/16)}xe2x80x3 depending upon the skill of the operator and the degree of care expended by the operator. The current system does not produce repeatable results within tolerance limits typically desired for fit-up and assembly of aircraft components. When controlled tolerances are required, additional manufacturing operations must be included.
Currently, when accuracy is required in the location of a joggle, a workpiece having an excess of material is positioned in the die assembly and the joggle is formed in the workpiece in the conventional manner. After removal of the joggled workpiece from the die assembly, the excess material is then machined from the workpiece and the workpiece is measured to determine the proper location of the joggle, and re-machined as required.
What is needed is an accurate, repeatable system to position a workpiece formed of extruded metal or shaped sheet metal in a die system for forming joggles that reduces the inaccuracies inherent in the current system in aligning the workpiece, allowing for repeatable and precise alignment of the workpiece in relation to the die system.
The present invention provides an apparatus and a method for accurately and repeatably positioning metallic parts comprised of variable length extrusions and shaped sheet metal in a modular die system that forms a joggle in the metallic parts.
The apparatus of the present invention is comprised of a standard joggle die system that is currently in use in the art. The joggle die system permits a joggle to be formed in a metallic part. These metallic parts or workpieces are extrusions or shaped sheet metal parts that require additional metal forming operations so that they can be used for specific applications.
A joggle is an offset that is placed in a workpiece, typically an extrusion. It provides a work surface that is out of the plane of the original work surface. While there is no requirement that a joggle provide a work surface that is parallel to the work surface of the original workpiece, a joggle typically does offset the surface to provide such a parallel workpiece. The joggle typically is formed near the end of the workpiece and permits the offset plane formed in the workpiece to be mated with another workpiece, thereby allowing the parts to be joined by a manner such as by riveting or bolting. The offsets are formed by application of pressure by means of a set of forming dies in a press. The forming dies can be arranged to change the depth of the offset or joggle. Rotation of portions of the dies can also change the radius of the joggle, as can the shape of the dies. Joggles can be formed in a variety of materials having different thicknesses. Joggles have been formed in materials in thicknesses of up to one inch. As the thickness of the material increases and as the tensile strength of the material increases, the pressure required to form a joggle becomes greater and the strength requirements of the dies increases. While joggles may be formed in materials such as aluminum and titanium in thicknesses of up to one inch, more typically joggles are formed in materials having thicknesses of about xe2x85x9xe2x80x3 and less.
The present invention utilizes a back gage assembly in combination with the joggle die system to permit accurate placement of the joggle in the workpiece. The back gage assembly includes a movable back gage plate. The back gage plate is movable in a horizontal direction and in a vertical direction. The joggle die system includes at least a pair of movable dies that can be moved from an open position for receiving and removing the workpiece, and a closed position for retaining the workpiece. Clamps may be utilized to grasp the work piece to prevent movement of the workpiece in the dies during the joggle forming operation, or the dies solely may provide the required clamping force. The die assembly may include at least one heating element for heating the die system to a preselected temperature. Upon placing the workpiece in the die system for a preselected period of time, heat will be transferred from the dies to the workpiece to elevate the temperature of the workpiece so that the joggle operations can be a hot working operation. However, the joggle may be formed at room temperature, if required.
The back gage plate is movable in a horizontal direction from an open or stored position to a predetermined position that is related to the dies, and the back gage plate itself may be attached to a movable elongated member. This predetermined position determines the workpiece location at which the joggle will be formed. Before the workpiece is clamped between the dies, the back gage plate is moved to a predetermined position by a means that will accurately position the back gage plate in a horizontal direction and thereby accurately locate the workpiece between the dies. The vertical position of the back gage plate is adjusted by means that will position the back gage plate in a vertical direction so that it can contact at least one surface of the workpiece, but so that it is out of contact with the dies. After the workpiece is brought into contact with the back gage plate, the workpiece is firmly clamped into position and the back gage plate is moved horizontally to a stored position in which it is retracted away from the dies.
After the workpiece has been firmly clamped into position, the joggle die assembly can be activated to apply pressure to the workpiece and form a joggle in the die accurately at a preselected position of the workpiece.
An advantage of the present invention is that the back gage assembly permits accurate location of the joggle in the workpiece. The back gage assembly also permits a repeatable location of the joggle assembly in a plurality of workpieces. This accurate and repeatable positioning of the workpiece in the die assembly by the back gage assembly eliminates operator error previously associated with the positioning of the workpiece in the die assembly, thereby reducing scrap.
A further advantage of the present invention is that the back gage assembly increases productivity. In addition to the reduction of scrap due to operator error in placement of the workpiece in the die assembly, the amount of time spent in properly locating the workpiece in the die assembly is also reduced, so that the number of pieces that can be processed in a unit time can be increased.
Still another advantage of the present invention is that a machining operation utilized to precisely locate the joggle in an oversized workpiece can be eliminated. The elimination of this operation will also further increase the productivity as a time consuming precision machining operation can be eliminated.
Yet another advantage of the present invention is that the operator no longer required to place his hands between the hot forming dies in order to accurately align the workpiece with a scale. Not only is the possibility of contact with the hot dies significantly reduced, but also the positioning of the operator""s hands between potential pinch points and subsequent injury doe to machine malfunction or inadvertent activation is eliminated.
Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.